JP2012533257A - Method for selecting channel estimation method and radio receiver - Google Patents

Abstract

The wireless receiver receives a reference signal via a wireless link. The radio receiver calculates a selection index based on the received reference signal, and the radio receiver selects one of a plurality of channel estimation schemes based on the selection index. The selected channel estimation scheme can be used to perform channel estimation for the radio link.

Description

  The present invention relates at least to a method for selecting a channel estimation scheme and a radio receiver.

  Various radio access technologies (systems) have been proposed or implemented that allow a mobile station to communicate with other mobile stations or with a wired terminal coupled via a wired network. Specific examples of radio access systems include systems such as GSM (Global System for Mobile communication) and UMTS (Universal Mobile Telecommunications System) defined by the 3rd Generation Partnership Project (3GPP), CDMA2000 (Code Division Multiple Access 2000). CDMA2000 defines a kind of packet-switched radio access network, also referred to as HRPD (High Rate Packet Data) radio access network.

  Another recent standard for providing packet-switched radio access networks is the 3GPP Long Term Evolution (LTE) standard, which is intended to improve the UMTS system. The LTE standard is also referred to as the EUTRA (Evolved Universal Terrestrial Radio Access) standard. The EUTRA system will be the fourth generation (4G) system that wireless network operators are currently migrating to provide improved services.

  An object of the present invention is to provide an improved method and radio receiver for selecting a channel estimation scheme.

The method according to one embodiment comprises:
The wireless receiver receives the reference signal via the wireless link,
Calculating a selection index based on the reference signal received by the wireless receiver;
The wireless receiver has a step of selecting one of a plurality of channel estimation schemes based on the selection index, and the selected channel estimation scheme can be used to perform channel estimation of the radio link; There is a way.

1 is a block diagram illustrating an example system that includes a wireless communication network that can be used in one embodiment. The figure which shows the sub-frame structure in which the reference signal for a demodulation which can be used with the method by one Embodiment is contained. 5 is a flowchart illustrating a method for performing selection according to an embodiment from a plurality of channel estimation schemes for performing channel estimation. The figure which illustrates the response characteristic of the reference signal for a demodulation. The figure which illustrates the response characteristic of the reference signal for a demodulation.

  In general, a wireless receiver according to one embodiment receives a reference signal via a wireless link. The radio receiver calculates a selection index based on the received reference signal, and the radio receiver selects one of a plurality of channel estimation schemes based on the selection index. The selected channel estimation scheme can be used to perform channel estimation for the radio link.

  Other or alternative features will be apparent from the following detailed description, drawings, and claims.

  Embodiments will be described below with reference to the drawings.

  Radio link channel estimation is used to determine the channel response of the radio link and to be able to eliminate or reduce the effects of interference in the radio link. Accurate channel estimation allows the performance of wireless communications in wireless networks to be improved, for example, by means of a high data rate format and / or a format with less error due to interference.

  A plurality of channel estimation techniques may be used when performing channel estimation. However, various channel estimation techniques are not always optimal under various conditions. For example, one type of channel estimation technique is based on the use of time domain averaging algorithms, which work well when the mobile station is moving relatively slowly, but the speed There is a possibility that it does not work well in a high situation. Another type of channel estimation technique uses an algorithm that performs linear interpolation in the time domain, which works well in fast situations (where the mobile station is moving relatively fast), but in slow situations However, it may not work well in a noisy situation.

  According to one embodiment, techniques, techniques, methods or means are provided that enable real-time estimation of radio link conditions so that real-time switching can be performed among various channel estimation schemes. Real-time switching or switching among different channel estimation schemes determines the channel state within a specific time interval (time interval), and different channels within the same time interval based on the determined channel state. The function to switch the estimation method is shown.

  In one embodiment, the determination of channel conditions to perform switching between channel estimation schemes is based on reference signals received over the radio link. In one embodiment, the reference signal is a reference signal for demodulation (DMRS), which is a reference signal used to enable coherent signal demodulation at the wireless receiver. As an example, the reference signal for demodulation is associated with transmission of uplink data and / or control signaling (data and / or control signaling transmission from the mobile station to the base station). The reference signal for demodulation is time-multiplexed with the uplink data. The demodulation reference signal facilitates estimation of the channel response to the uplink data so that the uplink channel can be efficiently demodulated.

  Although reference signals for demodulation are discussed in the present description, techniques, methods or means according to embodiments of the present invention may be used with other reference signals in the uplink. More generally speaking, a “reference signal” is a control signal that includes information for the radio receiver to properly process information received via the radio link. Note that although uplink reference signals are discussed, in alternative embodiments, other types of reference signals may be transmitted on the downlink (base station to mobile station). The techniques, methods or means according to embodiments of the present invention that allow switching between different channel estimation schemes based on the determined channel conditions are applicable to both uplink and downlink.

  FIG. 1 shows an example system including a radio communication network with an EUTRA (Evolved Universal Terrestrial Radio Access) radio access network 102. The EUTRA standard is also referred to as the LTE standard and is defined by the 3rd Generation Partnership Project (3GPP). The EUTRA radio access network 102 includes a base station 103, and in the case of EUTRA, the base station is referred to as enhanced node B (eNodeB, eNB). Base station 103 can perform wireless communication with mobile station 108 via wireless link 104. Although only one base station 103 and only one mobile station 108 are shown in FIG. 1, it should be noted that there are generally a plurality of base stations and mobile stations in a wireless communication network.

  The base station can perform, for example, one or more of the following tasks: radio resource management, mobility management to manage mobile station movement, traffic routing, etc. In general, the term “base station” refers to any type of wireless transmitter / receiver that communicates with a cellular network base station or access point or mobile station used in any type of wireless network. The term “base station” can encompass a base station controller or an associated controller such as a radio network controller. The term “base station” is intended to indicate a femto base station or access point, a macro base station or access point, a pico base station or access point, and the like. A “base station” may refer to a telephone handset, a portable computer, a personal digital assistant (PDA) or an embedded device (eg, a hesle monitor, attack alarm, etc.).

  As shown in FIG. 1, the mobile station 108 is connected to the base station 103 wirelessly. The base station 103 is connected to various elements including a serving gateway 110 and a mobility management entity (MME) 112. The MME 112 is a control node in the EUTRA access network 102. For example, the MME 112 performs tracking and paging processing of the mobile station in the idle mode. The MME 12 performs a process of selecting a serving gateway for the mobile station at the time of the first attach and the time of the handover. The MME 112 also performs processing for authenticating the user of the mobile station.

  Serving gateway 110 routes bearer data packets. The serving gateway 110 functions as a user plane mobility anchor during handover between different access networks. The serving gateway 110 is also connected to a packet data network (PDN) gateway 114 that provides a connection between the mobile station 108 and the packet data network 116 (eg, a network that provides various services, the Internet, etc.).

  The EUTRA standard is intended to indicate a standard that evolves over time in addition to the current EUTRA standard. It is expected that future standards developed from EUTRA may be referred to by different names. “EUTRA” is intended and considered to encompass such standards that will evolve in the future.

  Although referred to as EUTRA, the techniques, methods, or means according to one embodiment are also applicable to systems that utilize other types of wireless protocols.

  Still referring to FIG. 1, the base station 103 includes a radio receiver 120 for receiving radio information (bearer data and control signaling) via the radio link 104. Radio receiver 120 includes a channel estimation logic unit 122 (performing radio uplink channel estimation) and a channel estimation scheme switching logic unit 124 (performing switching between channel estimation schemes according to one embodiment). In one embodiment, each of the logic units 122 or 124 may be implemented by an associated hardware circuit or may be a processor (eg, a microprocessor, microcontroller, revenue circuit, or other hardware processing device). It may be implemented by executable machine readable instructions. Within the figure, the mobile station 108 may also include a radio receiver, and the radio receiver may also include a channel estimation logic unit and a channel estimation scheme switching logic unit similar to those in the radio receiver 120.

  FIG. 2 shows an example of an uplink subframe structure 200, which corresponds to TTI (Transmission Time Interval) in EUTRA. The uplink subframe structure is defined by time along one axis and frequency along the other axis. Different frequencies correspond to different subcarriers (SC) starting from SC0 and ending at SCn-1. The white square portion of the uplink subframe structure 200 carries data, and the shaded square portions 202 and 204 carry symbols for a reference signal (DMRS) for demodulation. DMRS symbol 202 is at symbol position 3 in subframe structure 200, while DMRS symbol 204 is at symbol position 10 in subframe structure 200.

  In order to determine the channel state for the purpose of switching the channel estimation scheme, the channel information received by the two DMRS symbols 202 and 204 is used in units of TTI. The channel information extracted from DMRS includes two-dimensional channel information over both the time domain and the frequency domain. By using the two received DMRSs included in each TTI (represented by the uplink subframe structure 200 in FIG. 2), real-time channel conditions can be determined, and multiple channel estimation schemes can be determined. Switching in can be performed every TTI.

  FIG. 3 is a flowchart of a method executed by the channel estimation scheme switching logic unit 124 shown in FIG. The channel estimation scheme switching logic unit 124 receives two DMRS symbols 202 and 204 in each subframe structure 200 (302 in FIG. 3). Based on the DMRS symbol, DMRS processing is performed to calculate a selection indication (304). In one embodiment, the selection indicator takes the form of a parameter referred to as Z in the current example. The channel estimation method switching logic unit 124 determines the state of the parameter Z (306). If Z has a first value (e.g., Z = 1), frequency domain noise reduction processing is performed (308), and a linear interpolation algorithm is selected to perform channel estimation (310). .

  On the other hand, if Z has a second value (eg, Z = 0), tasks 312 and 314 are performed, task 312 includes frequency domain noise reduction processing, and task 314 performs channel estimation. Selecting an averaging algorithm for the purpose.

  As shown in FIG. 3, after a selected one of the linear interpolation algorithm and the moving average algorithm is performed, an estimated channel response value is output to provide a channel estimation output ( 316). Note that in the example being described, only two different types of channel estimation algorithms are shown, but in alternative examples alternative or additional channel estimation algorithms may be used.

  The frequency domain noise reduction process performed at 308 or 312 in one embodiment may be based on a frequency domain moving average. The noise reduction process is used to reduce noise so as to provide a good channel estimation result. As shown in FIG. 3, the process of the logic unit included in the process of performing frequency domain moving averaging is generally represented as 320, and is input for frequency domain moving averaging. Is expressed by “input (IN)”, and the output of the moving average in the frequency domain is expressed by “output (OUT)”. A block “D” represents a delay block, and a circled x represents a multiplier (in the example shown in FIG. 3, 1/5 is multiplied). The five multiplied signals are provided to the adder and provide an output. In the case of the example in FIG. 3, N = 2 is selected for the moving average processing in the frequency domain, and the filter order in this case is 5. In other examples, other types or other orders of filters may be used with different values of N.

The parameter Z is calculated as follows:
Z = sgn (F (dmrs1, dmrs2) -delta) (Eq.1)
In this case,
When x> 0, sgn (x) = 1, and when x <0, sgn (x) = 0. (Eq.2)
F (*) is a function of dmrs1 and dmrs2 (eg, DMRS symbols 202 and 204 in FIG. 2), each of which contains M tones, respectively, as follows:
dmrs1 = {h1 ₀ , h1 ₁ , ..., h1 _M-1 } (Eq.3)
dmrs2 = {h2 ₀ , h2 ₁ , ..., h2 _M-1 },
Delta is a design parameter determined by simulation or testing.

According to one embodiment, each of the two DMRS symbols provides a channel frequency response with noise added at a particular time in a subframe. The actual relationship between channel frequency response and noise is complex, but for simplicity of analysis, the relationship is derived from the channel frequency response of the i th subcarrier, denoted as h _i , and the associated noise sample. Suppose that it can be approximated by the summation with n _i . That is,
d _i ^k = h _i ^k + n _i ^k i = 0,1, ..., M and
k = a (for DMRS1) and k = b (for DMRS2)
However, M is the number of subcarriers used, and the amount used here is a complex number.

  4A and 4B show examples of frequency responses of DMRS202 (DMRS1) and DMRS204 (DMRS2), respectively. As shown, it can be clearly seen that the responses of the two DMRS1 and DMRS2 are different. The difference between the two DMRS symbols is used to represent channel conditions and allow switching between channel estimation schemes to be performed according to one embodiment of the invention.

  In a wireless environment, the channel frequency response exceeds “temporal variations” due to mobile station movement. Since there is a time offset between DMRS1 and DMRS2 in each subframe, its “temporal variation” is the two received (for example, as shown in FIGS. 4A and 4B). It should reflect differences or differences between DMRS symbols. If a quantity (eg, Z) has been selected to evaluate this difference, that quantity can be used to see how much channel variation is occurring along the time axis.

  In one embodiment, the average of each DMRS sequence is selected as a quantity to evaluate the overall state of each DMRS, and the difference in state between the two DMRS symbols is determined by the channel in the time interval between the two DRMS symbols. It is selected as an amount to evaluate the change in DMRS2 relative to DRMS1 due to frequency response variation. Thus, by way of example, the given number F (*) above can be expressed as:

数式Eq.4及びEq.5における第2項は平均化に起因するノイズ低減効果を反映しており、元のノイズ電力からのノイズ電力の低減及びDMRS各々の平均推定値の改善をもたらすことに留意を要する。Mが大きな値であるほど、より正確な推定を行うことができる。

The second term in Equations Eq.4 and Eq.5 reflects the noise reduction effect due to averaging, which leads to a reduction in noise power from the original noise power and an improvement in the average estimate for each DMRS. Need attention. The larger M is, the more accurate estimation can be performed.

  In the above description, numerous details are set forth to facilitate understanding of the invention disclosed by the present application. However, embodiments may be realized without relying on all or part of such details. From the above detailed description, other embodiments include modifications and variations. The appended claims are intended to cover such modifications and variations.

Claims (23)

The wireless receiver receives the reference signal via the wireless link,
Calculating a selection index based on the reference signal received by the wireless receiver;
The wireless receiver has a step of selecting one of a plurality of channel estimation schemes based on the selection index, and the selected channel estimation scheme can be used to perform channel estimation of the radio link; There is a way. When receiving the reference signal, receive a demodulation reference signal,
2. The method according to claim 1, wherein the calculation of the selection index is based on the reference signal for demodulation.   2. The method of claim 1, wherein the calculation of the selection index is based on determining an amount that reflects a difference between the reference signals.   4. The method of claim 3, wherein the quantity is based on a sum of channel frequency responses at multiple frequencies.   5. The method of claim 4, wherein the quantity is based on a sum of channel frequency responses at a plurality of frequencies and associated noise samples.   2. The method according to claim 1, wherein when receiving the reference signal, a reference signal in an EUTRA (Evolved Universal Terrestrial Radio Access) scheme is received.   2. The method of claim 1, wherein the wireless receiver is part of a base station or mobile station.   2. The method of claim 1, further comprising the wireless receiver performing channel estimation using the selected channel estimation scheme.   9. The method of claim 8, further comprising performing frequency domain noise reduction processing before performing channel estimation using the selected channel estimation scheme.   2. The method according to claim 1, wherein when selecting any one of the plurality of channel estimation methods, a selection is made from an averaging algorithm and an interpolation algorithm.   The method of claim 1, wherein the reference signal is within a specific time interval and the other time intervals include a group of other reference signals. A wireless receiver having a channel estimation method switching logic unit, wherein the channel estimation method switching logic unit is
Receiving a reference signal transmitted over the radio link,
Calculate a selection index based on the received reference signal,
Select one of a plurality of channel estimation methods based on the selection index,
The selected channel estimation scheme can be used to perform channel estimation of the radio link;
The channel estimation method switching logic unit is a radio receiver including hardware.   13. The radio receiver according to claim 12, wherein the reference signal includes one of an uplink reference signal and a downlink reference signal. The reference signal includes a reference signal for demodulation;
13. The radio receiver according to claim 12, wherein the selection index is calculated based on the demodulation reference signal.   13. The wireless receiver according to claim 12, wherein the selection index is calculated based on determining an amount that reflects a difference between the reference signals.   16. The wireless receiver of claim 15, wherein the quantity is based on a sum of channel frequency responses at multiple frequencies.   17. The wireless receiver of claim 16, wherein the quantity is based on a sum of channel frequency responses at a plurality of frequencies and associated noise samples.   13. The radio receiver according to claim 12, wherein the reference signal includes a reference signal in an EUTRA (Evolved Universal Terrestrial Radio Access) system.   13. The radio receiver according to claim 12, further comprising a channel estimation logic unit that performs channel estimation using the selected channel estimation scheme.   20. The radio receiver according to claim 19, further comprising a logic unit that performs noise reduction processing in a frequency domain before performing channel estimation using the selected channel estimation scheme.   13. The wireless receiver of claim 12, wherein the reference signal is within a specific time interval and the other time intervals include a group of other reference signals.   A base station comprising the radio receiver according to claim 1.   A mobile station comprising the radio receiver according to claim 1.

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